James D. Jorgensen (1948–2006)

Pioneer of neutron diffraction and the structure of superconductors.

Credit: ARGONNE NATIONAL LABORATORY

When Jim Jorgensen wished to refocus the attention of a post-doc after the presentation of a 'novel' result he would say in a jovial but gentle manner “...nothing simulates a new effect quite like a mistake”. In many ways, this anecdote exemplifies Jorgensen's clarity of mind, a quality that allowed him to develop neutron powder diffraction at spallation sources from a little-appreciated curiosity into a powerful investigative tool, which he then went on to apply, with extraordinary results, to the study of the structure–property relations of a variety of materials. Jorgensen's contribution has perhaps been most influential in the field of superconductivity, where he produced authoritative and highly cited papers on virtually all superconductors of the past 30 years. However, his wider legacy in neutron powder diffraction, crystallography, materials physics and solid-state chemistry is as relevant now as at any time in his career, as the scientific case for the next generation of spallation neutron sources in the US and Japan is based to a large extent either directly on his work or indirectly on the example and inspiration he was able to set.

Jorgensen, who died on 7 September 2006, was a great believer in ideas and recognized opportunity at first sight. At the time of his entry into the world of neutron scattering, neutron powder diffraction was viewed as a mature technique, firmly established at nuclear reactor-based neutron sources and using instrumentation closely related to conventional X-ray diffractometers. Therefore, by the standard of the 1970s, Jorgensen had an unconventional approach to the technique, which would later define his main contributions to neutron science. As a young scientist at Argonne National Laboratory's CP-5 reactor, he used the 'exotic' time-of-flight technique, coupled with fixed-angle detectors, to study the structure of materials under high pressure.

Jorgensen soon realized that the fledgling development of spallation neutron sources, which was taking place just down the road from CP-5, offered tantalizing opportunities for neutron powder diffraction, far beyond the field of high-pressure physics. He held a strong belief, amidst general scepticism, that diffraction at these new, exceedingly 'weak' sources could compete with and in some cases exceed what is possible at reactors. Working with Jack Carpenter, Bob Klebs and others, he built, quite literally, the first time-of-flight diffractometers at spallation sources and later designed and constructed the second generation neutron diffractometers at Argonne's Intense Pulsed Neutron Source.

In spite of these brilliant achievements, Jorgensen was never just an instrument builder. His prime motivation was always to apply the capabilities of his new tools to materials physics. Ever sensing new opportunities, he formed what would become a life-long partnership with a brilliant young chemist, David Hinks. Together, they hunted for highly topical problems where the underlying physics was obscured by chemistry and materials issues. Combining sophisticated, high-quality solid-state synthesis with state-of-the-art neutron crystallography they almost always brought instant clarity to the community. This strategy was applied perhaps most successfully to the field of superconductivity. As the research focus shifted from relatively simple metallic alloys to complex, multicomponent materials, crystal and defect chemistry took centre stage, and so did neutron powder diffraction. Jorgensen and Hinks played a leading role in the seminal paper on the crystal structure of the superconductor YBa₂Cu₃O_6+x — a truly historic event in high-temperature superconductivity, because to everyone's surprise, the structure did not contain CuO₆ octahedra. Later, they produced a series of classic papers on the effect of oxygen doping on the properties of superconductors and many other materials.

Building on his vast experience, Jorgensen was equally prolific in producing long-lasting ideas, relating theoretical concepts to actual materials. For example, he was the first to find phase separation in the superconductor La₂CuO_4+δ, and guided by the theoretical insight of Vic Emery and many others, proposed that this could reflect an intrinsic tendency to electronic segregation. Fifteen years later, the concept of electronic phase segregation is still very much at the centre of the theoretical and experimental debates.

Jim Jorgensen was interested in people as much as ideas. He was a mentor to many young scientists. However, he had a peculiar style in choosing his collaborators. For example, he once boasted of having chosen as a post-doc a young scientist, among many with an excellent resumé, because he played the drums and practised rock climbing. To Jim, this was a clear indication that he had 'fire in the belly', an assessment that was later proven uncanningly accurate. Jim was an amateur radio enthusiast and used a 10-metre antenna in his yard to communicate with people from around the world, especially before a visit to their country. His interest in people was complemented by his strong sense of community, and his talents in building and nurturing communities were a gift to physics and crystallography in the US and beyond. When the US Department of Energy (DOE) described the US neutron community as “small and fractious”, Jim worked tirelessly behind the scenes to bring people together. The fact that only a few years later the DOE funded the $1.4 billion Spallation Neutron Source (SNS) project is a testament to Jim's gentle use of persuasion and reason to bring people together. It is therefore immensely sad that the SNS will have to begin its scientific commissioning without him.